The present disclosure relates in general to pleated filter media and, in particular, to pleated adsorptive depth filter media for filtering fluids and to the filter cartridges utilizing such pleated filter media.
Filtration is the process of separating particles or contaminants from a fluid (liquid or gas), and can be accomplished by passing the fluid through porous filter media that stops or captures the particles while permitting the fluid to pass therethrough. Most conventional filter media may be categorized into two broad categories: surface-type filter media, which stops fluid contaminants on its surface, and depth-type filter media, which captures contaminants within the medium, i.e. between an upstream surface and a downstream surface of the medium.
Depth-type filter media and, in particular, adsorptive depth filter media, have long been known. Adsorptive depth-type filter media use a variety of materials for filtering fluids, including cellulose and any of a variety of adsorber particulate matter. Other materials, such as glass fibers or synthetic fibers (for example, polypropylene fibers or polyethylene fibers), may be included. Known adsorptive depth-type filter media typically include between 30% to 50% cellulose, although the cellulose may comprise as little as 10% by weight of the total. Known depth filter media also typically include between 50% to 70% by weight of particulate adsorber matter. Filter performance is enhanced by maximizing the amount of fine adsorber particulate matter in the depth filter media layers. Known adsorber particulates that are suitable for the intended purpose, include diatomaceous earth (i.e. an earth having friable dust like silica of diatomaceous origin), perlite, talc, silica gel, activated carbon, asbestos, molecular sieves, clay, etc. For the most part, these adsorber particles have diameters of less than 10 microns. Siliceous materials, such as diatomaceous earth or perlite, are commonly used. Furthermore, it is known that adsorptive particulate materials may be impregnated with other chemicals for providing or enhancing selective adsorption characteristics. Additionally, depth filter media may include binder resins.
Commonly, such adsorptive depth filter media have been used in lenticular-type stacked disc filter elements (as illustrated in U.S. Pat. No. 6,712,966, the disclosure of which is incorporated herein by reference to the extent not inconsistent with the present disclosure). Adsorptive depth filter media require a reasonable flow-through thickness in order to provide the contaminants sufficient contact opportunity to be adsorbed by the filter medium and to effectively remove contaminants from a fluid stream. Typical thicknesses for depth-type media have ranged from 2500 to 7500 microns thick. For a given filter volume displacement of a lenticular-type filter unit composed of a plurality of lenticular cells, the maximum surface area and media packing density are limited due to the thickness of support separators found inside the cells and the space between cells necessary to permit acceptable flow rate.
Pleating is recognized as one approach to achieving a high media packing density in a given filter volume. Pleated filters are typically made with relatively thin cellulosic or synthetic surface-type filter media folded in an accordion-like fashion. In a cylindrical radial-pleated type filter element there may be a significant degree of spacing between outer tips of the pleats. Spiral pleat filters (see U.S. Pat. No. 6,598,749, the disclosure of which is incorporated herein by reference to the extent not inconsistent with the present disclosure) and multiple rings of concentrically located pleated filter elements (see U.S. Pat. No. 5,232,595, the disclosure of which is incorporated herein by reference to the extent not inconsistent with the present disclosure) have been used to reduce this outer tip spacing and increase the filtering surface area. U.S. Pat. No. 6,315,130 to Olsen, which issued Nov. 13, 2001, and which is hereby incorporated by reference to the extent not inconsistent with the present disclosure, teaches using pleats of varying height to increase the pleat density at the outer diameter of the cylindrical filter and to increase the filtering surface area. It is also known to use different layers of filter media in a filter cartridge in order to increase the depth of the media and to impart different filtration characteristics at each layer.
Pleating requires tight bending radii, i.e. that the filter media bend sharply to form the pleats. For this reason, pleated filters have typically been formed with relatively thin, flexible cellulosic or synthetic surface-type filter media, rather than with the thicker adsorptive depth filter media. Surface-type filter media, which include meltblown, needle-felted, or spunbonded polymeric media, wet laid or air laid glass fiber media, cellulosic fiber media which may be resin impregnated, micro-porous polymeric membrane, metal fiber or perforated metal media, and any combinations above, have been used for pleating. These surface-type filter media lack the highly desirable particulate adsorbers found in adsorptive depth filter media.
However, adsorptive depth-type filter media, which incorporate such particulate matter, are brittle and typically cannot withstand the elongation at the bend radii when pleated. For example, when an attempt was made to pleat a cellulosic filter media having a high amount of particulate adsorber material (about 60% or greater of diatomaceous earth) and having a thickness of about 3.56 mm, the filter media cracked. The cracking is a result of the filter media's structure and its rigidity caused by the high amounts of diatomaceous earth (DE). Due to the structure of the fibers in the filter media, the entire thickness of the media will bend in unison. Because the external bend radius for such a thick layer is significantly greater than the neutral bending radius, there is a high degree of tensile strain along the external bend radius. Also, because the internal bend radius is significantly smaller than the neutral bending radius, there is a high degree of compressive strain along the internal bend radius. Cracking and splitting of the fibers in the filter media is the inevitable result of these high strains because the filter media contains high amounts of particulate adsorbers and low amounts of cellulose. The thicker the filter media, the greater the difference is between external and internal bending radius, leading to high filter media elongation at the external radius and high filter media compression at the internal radius. Thus, pleating conventional adsorptive depth filter media causes the filter media to crack or tear, thereby losing both filtering ability and structural integrity. Lenticular-type stacked disc filter elements avoided this problem by not bending the depth-type filter media.
U.S. Pat. No. 5,232,595 to Meyer, the disclosure of which is incorporated herein by reference to the extent not inconsistent with the present disclosure, discloses pleated adsorptive depth-type filter media. Specifically, Meyer discloses a deep bed pleated filter with an individual filter media layer thickness of at least 1 mm. Meyer further discloses that adsorptive depth-type filter media can be pleated provided that the particulate adsorber content is 50% or less by dry weight.
There is a need for high media packing density in an adsorptive depth-type filter module. High packing density in an adsorptive depth-type filter media provides improved filtration efficiency. There is also a need for increased surface area for a given media mass in an adsorptive depth-type filter module. Increased surface area for a given media mass provides higher flow rate. Thus, both high media packing density and increased surface area are important in an adsorptive depth-type filter. Typically, however, there is a trade-off between achieving these desirable filter characteristics. Thus, there is a need for an adsorptive depth-type filter module that has high media packing density without sacrificing surface area. Further, there is a need for an adsorptive depth-type filter module that allows the fluid to be filtered to substantially access the entire filter media. The present state of the art does not allow the use of adsorptive depth filter media in high media density pleat designs, such as disclosed in Olsen, and as a result high media packing density has not been achieved in adsorptive depth-type filter modules. The present art also has problems associated with wet weight. After the lenticular cartridges are used the added weight due to the media being wet makes it cumbersome to handle. In addition the lenticular style cartridges also have many parts which contribute to the total weight of the cartridge. Another problem with the lenticular style cartridges becomes the size, when larger quantities of fluid need to be filtered, larger diameter lenticular cartridges are used, these lenticular cartridges both use more floor space and also makes it more difficult to handle due to cartridge size.